The present invention relates to a separator. In particular, the present invention relates to a separator for separating particulate, liquid and aerosol contaminants from a fluid stream.
Blow-by gas within a reciprocating engine is generated as a by-product of the combustion process. During combustion, some of the mixture of combustion gases escape past piston rings or other seals and enter the engine crankcase outside of the pistons. The term “blow-by” refers to the fact that the gas has blown past the piston seals. The flow level of blow-by gas is dependent upon several factors, for example the engine displacement, the effectiveness of the piston cylinder seals and the power output of the engine. Blow-by gas typically has the following components: oil (as both a liquid and an aerosol, with aerosol droplets in the range 0.1 μm to 10 μm), soot particles, nitrous oxides (NOx), hydrocarbons and other organic species, carbon monoxide, carbon dioxide, oxygen, water, and other gaseous air components.
If blow-by gas is retained within a crankcase with no outlet, the pressure within the crankcase rises until the pressure is relieved by leakage of crankcase oil elsewhere within the engine, for example at the crankcase seals, dipstick seals or turbocharger seals. Such a leak may result in damage to the engine.
In order to prevent such damage, and excessive loss of oil, it is known to provide an outlet valve that allows the blow-by gas to be vented to the atmosphere. However, with increasing environmental awareness generally, and within the motor industry in particular, it is becoming unacceptable to allow blow-by gas to be vented to atmosphere due to the discharge of oil and other contaminants from within the crankcase. Furthermore, such venting increases the speed at which crankcase oil is consumed.
Consequently, it is known to filter the blow-by gas. The filtered blow-by gas may then either be vented to the atmosphere as before (in an open loop system), or it may be returned to an air inlet of the engine (in a closed loop system). The blow-by gas may pass through a filtering medium or another known form of gas contaminant separator. The conventional arrangement of an engine blow-by gas/oil separator returning cleaned gas to an engine air intake is commonly referred to as a Closed Crankcase Ventilation (CCV) system.
There is an increasing demand for higher efficiency cleaning of blow-by gas in both open and closed loop systems. Engine manufacturers and end users in general prefer only to use engine components that can remain in place for the life of the engine. While fit-for-life separators are known, typically only powered centrifugal separators and electrostatic precipitators have hitherto been able to achieve the required levels of separation efficiency. Such separators are costly to manufacture, consume electrical power, or have moving parts which may be prone to wear. Low cost, fit-for-life impactor separators (where separation occurs as a contaminated gas stream is incident upon an impactor plate transverse to the gas flow) are not usually able to achieve the required separation efficiency. Impactor separators are also referred to in the art as inertial gas-liquid impactor separators. It is known to use inertial gas-liquid impactor separators in closed crankcase ventilation systems. Contaminants are removed from the fluid stream by accelerating the fluid to a high velocity through a slit, nozzle or other aperture and directing the fluid stream against an impactor plate to cause a sharp directional change.
WO-A-2011/095790 discloses a separator for separating contaminants from a fluid stream using an inertial impactor surface. Contaminated blow-by gas flows from a regulator chamber through an aperture in a wall of the chamber so that it is directed against an impactor surface. The aperture tapers from a wide end at the top of the wall to a narrow end. The separator includes a diaphragm which slides along the wall so as progressively to cover and to uncover the aperture, varying the open area of the aperture according to the pressure in the regulator chamber. The tapered shape of the aperture can help to eliminate pump-surge conditions.